• ER resident protein-O-fucosyltransferases [POFUT1/FUT12 and POFUT2/FUT13] that attach alpha-Fuc to hydroxyl of Ser/Thr at specific consensus sequences of epidermal growth factor (EGF)-like repeats (added by POFUT1) and thrombospondin type 1 repeat (TSR, added by POFUT2).
• Putative consensus sequences for O-fucosylation in EGF repeats [C2-X-X-X-X-(S/T)-C3] and TSRs [C2-X-X-(S/T)-C3-X-X-G] have been defined, where Cx refers to the position of one of the conserved cysteines within the domain and S/T is the site of modification.
• Thus, these enzymes may fucosylate ~100 EGF repeat structures (by POFUT1) and ~30 TSRs (by POFUT2). EGF repeats of proteins bearing O-Fuc include tissue-type plasminogen activator, Factor VII, Factor IX, Notch, Delta, Serrate, Jagged, and Cripto. Examples of TSR1 modified proteins include members of the disintegrin and metalloprotease domain with thrombospondin type 1 repeats family (e.g., ADAMTS 5 and 13) and ADAMTS-like family (e.g., ADAMTSL1; Wang et al. 2007).
• Mice lacking POFUT1 are embryonically lethal, and those without POFUT2 die at E7.5. Thus, both POFUT1 and POFUT2 play essential roles in development.
• POFUT1 plays a key role in regulating Notch dependent signaling.
• The O-fucose on Notch EGF repeats are extended by the Fringe family of β3-GlcNAcTs. They can be further extended to create Siaα2-3/6Galβ1-4GlcNAcβ1-3Fucα-O-Ser/Thr.
• O-Fucose on TSRs is typically found extended to the disaccharide Glcβ1-3Fucα-O-Ser/Thr This extension elongation is due to a β3-glucosyltransferase. Mutations in the β3-glucosyltransferase result in the human developmental disorder Peters plus syndrome. Both O-fucosylated and C-mannosylation occur on TSR1/thrombospondin-1.